In the field of cardiac medicine, minimally invasive therapies for treating conditions at the heart's external surface, or epicardium, have been developed or contemplated using epicardial leads. However, currently marketed epicardial lead designs have major drawbacks.
The first drawback is that current epicardial leads require a more invasive surgical approach to gain access to the epicardium and to be able to fixate the leads into the heart wall. The most minimally invasive conventional procedure is a video assisted thoracoscopic procedure (VATS), which is still considered a surgical method. It involves providing two access holes into the chest with the patient under general anesthesia. The first access hole is for the thoracoscope, which is placed in position to visualize the heart by reaching through the patient's left side and collapsing the left lung. The second access hole is used for the epicardial lead delivery. This approach is surgical in nature, requires anesthesia and puts the patient on single lung ventilation, all of which result in longer hospitalization, higher costs, higher morbidity and present the risk of other complications. Because of the nature of the access approach, this technique also limits where the leads can be placed, resulting in non-optimal placement of epicardial leads—e.g., intended left ventricular pacing.
The second drawback to conventional techniques is the securing of the lead in its intended position, which is with sutures in combination with active fixation type anchors. This involves trauma to the heart wall and, even though the fixation is into the tissue, there are still signal capture issues. As a result, it is not uncommon that two epicardial leads are implanted to help lower the signal capture thresholds. Lower signal capture thresholds are important to reduce power levels that affect battery life. Also, any time tissue such as the myocardium is penetrated, an inflammation response occurs, which is why conventional leads today have embedded steroids to manage the tissue response. The addition of a drug to the implant complicates the development, regulatory approval, and manufacturing of these leads. The anchoring methods described are similar to those used for endocardial leads and are one of two methods, where the anchors are integral to the electrodes to improve the signal measurement and delivery as much as possible. The first is a passive fixation method often described as a “fish hook” anchor that uses bristle-like tines on the lead to anchor the lead to the intra-cavitary pectinate muscles. The second is an active fixation method often described as a “screw-in” or “corkscrew” anchor. Endovascular leads, on the other hand, that go into small vessels such as the coronaries can have inherent winding curvatures or spirals intended to distend the vessel, to increase the frictional interaction and thereby help improve the electrical contact with the electrodes and provide positioning fixation of the lead. The St. Jude Quartet™ Quadripolar lead is an example of a commercially marketed lead with these spiral shape features. The epicardial space does not have such tissue constraints all around the leads.
The third drawback of current epicardial leads is that the number of contacts or electrodes is limited and local to attachment to the heart wall. Currently, there is only one site for pacing or sensing and it is generally done at the left ventricle epicardial location with permanent leads. However, often the therapy needs to be directed to multiple points, such as on atria and ventricles. Also, with only a few electrodes limited to a local region, there is no ability to implement advanced signal interpretation algorithms to improve therapy delivery—e.g., reducing inappropriate shocks for devices and leads with defibrillation. Since currently marketed devices have the primary electrodes integral or very near the fixation anchor, multiple epicardial leads must be used to get more than one electrode in contact with the heart wall. Bipolar epicardial leads are the only marketed examples today that exist (such as from St. Jude Medical or Greatbatch), which have a second electrode. However, it is in immediate proximity to the electrode anchored to the heart wall.
Examples of current epicardial lead products that have these aforementioned drawbacks include the CRT-Myopre lead by Greatbatch Medical and the Epicardial MP lead by Oscor Inc. Their use has been very limited due to these and other drawbacks.
With the introduction of new minimally invasive subcutaneous implantable cardioverter defibrillators (S-ICD's) there is an increased need for developing minimally invasive epicardial leads that do not require a surgical implantation approach. Subcutaneous ICD implantation has been the most recent advancement in ICD technology and has several advantages: it spares the higher risk intravascular approach, it provides access to the heart when intravascular access is not available or possible such as contra-indications like infection, and it leaves veins available for access for other indications. Although subcutaneous ICD devices have good sensing capabilities suitable for the intended ICD therapies such as defibrillation, there are many patients who are not ideal candidates as the ECG (electrocardiogram) criteria does not hold well for their candidacy. Also, current devices lack pacing capability. This limits their usefulness because the target patients for these devices have advanced heart conduction system disease even in the absence of heart block that requires pacing for heart rhythm management.
Endovascular based pacing leads have limitations as well. The current traditionally-placed coronary sinus leads used for endovascular left ventricle (LV) pacing for cardiac resynchronization are limited not just by the presence of coronary sinus branches and their caliber, but also by the challenges associated with implantation. Accordingly, outcomes are limited due to the limitations for pacing. Even leadless endovascular pacing devices have severe complication risks, including heart wall perforation and dislodgement.
Finally, there are no left atrial pacing or sensing systems which could enable right atrium to left atrium synchronization.
U.S. Pat. No. 8,942,827 contemplates a multi-electrode design based on a distributor housing from which branches of electrodes extend. However, it still requires fixation to the heart wall and therefore has similar drawbacks to current leads. U.S. Patent Publication No. 2007/0043412 also describes multiple electrodes along branches that extend outward. Here too, fixation of the multiple lead branches and electrodes poses significant challenges.
These epicardial lead examples and their associated implantation techniques are not well developed because they are surgical in nature and, consequently, more invasive. This, in turn, makes them less likely to be adopted and considered. In the past, electrode patches were used for pacing at multiple sites, which involves even more invasive sternotomy or thoracotomy procedures. Patches have largely been abandoned with the advent of intravenous leads that are far less invasive in comparison.
All the identified challenges have limited the implementation of epicardial leads. As such, what is needed is not just a multi-electrode lead but a single-lead multi-electrode construct that can be delivered with minimally invasive methods into the pericardial space using a catheter lumen, and that can be positioned across multiple areas of the epicardial surface of the heart without penetrating the heart wall or tissue.